Mobile stations that operate in Wireless Local Area Networks (WLANs) are often capable of engaging in multiple calls. For example, a first user at the mobile station may be engaged in an on-going voice call with a second user, another voice call from a third user may arrive at the mobile station of the first user, and the first voice call may be put on hold. After completing the call from the third user, the first user may switch back to the initial call (that had been placed on hold) and continue the first call with the second user.
Some WLANs are connected to other networks, such as a cellular networks or the Public Switched Telephone Network (PSTN). Mobile stations operate within WLANs and utilize various protocols and messages to communicate. In one example, some wireless systems use the Session Initiation Protocol (SIP) to enable communications between mobile stations. Specifically, certain messages such as SIP INVITE messages are exchanged between mobile stations to initiate and conduct communications between these devices.
Mobile stations are typically not stationary within WLANs or other networks. For example, if the mobile station is a dual mode cellular telephone, the phone typically moves within the WLAN and then between the WLAN and other networks. When the mobile station leaves the WLAN, it is handed off (or over) to the receiving network. Various messaging protocols and sequences have been developed to ensure that the transition occurs smoothly.
Previous systems, however, do not allow a user at a mobile station to switch between an active call and a call on hold while the user is handed out of the WLAN system. This inability to switch between calls when handing a mobile station out of the WLAN system results in unpredictability in service for users, potential lost calls, and user dissatisfaction with system performance.
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